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From: TSS ()
Date: March 28, 2007 at 9:31 am PST


Chair: Robert A. Cook, Bronx, NY

Vice Chair: Michele A. Miller, Lake Buena Vista, FL


Drs. Dean Goeldner and Tom Gidlewski, VS, APHIS, USDA, presented the APHIS-VS chronic wasting disease (CWD) program update. CWD has been discovered in free-ranging cervids in 11 states and 41 captive cervid herds in nine states. There are currently four infected elk herds and one infected white-tailed deer herd that have chosen to remain under quarantine instead of depopulate. In 2006, the CWD program depopulated one elk herd in the endemic area which turned out to be infected as well as a chronically infected white-tailed deer herd and a mixed elk and white-tailed deer herd for a total of approximately 110 animals. For the last three years, the program has paid for testing about 15,000 captive cervids per year. Demand for testing is expected to increase with the implementation of the program. The first infected free-ranging white-tailed deer was found in northwest Kansas in 2006. On the positive side, New York found no additional positive free-ranging cervids in 2006 but West Virginia found four additional animals in Hampshire County. Wisconsin continues to aggressively battle CWD with over 100,000 animals submitted for testing since 2000 and over 650 positive deer identified. The infected area appears to be largely limited to the original counties. Interestingly, the number of deer in the Wisconsin endemic area does not appear to be decreasing despite the large number of animals that have been removed. Colorado has stopped culling deer in "hot spots" as they believe that it was not very successful. Alberta,

Canada continues to find more positive white-tailed deer adjacent to the infected Saskatchewan areas.

Appropriate tissue collection and submission for CWD diagnosis includes obex, medial retropharygeal lymph nodes and palatine tonsils. Submission of an ear with the official eartag attached or submission of fresh tissue accompanied by an appropriately executed chain of evidence document will allow DNA comparison in the event of a positive diagnosis. Archiving herd blood samples on special collection cards is also a way to compare DNA in the event of a positive diagnosis in the future. All positive cases are verified by two pathologists and the presumptive positive tissues are completely retested at the National Veterinary Services Laboratory (NVSL). Rectal biopsy continues to be examined as a tool for CWD ante-mortem diagnosis. Hundreds of animals have been examined and the results look promising. Larger numbers need to be examined in order to make final conclusions. Retrospective epidemiologic analysis and transgenic mouse research in 2006 still support the theory that CWD does not appear to affect people or non-cervids animals.

APHIS received approximately $18.5 million in appropriated CWD funding in FY 2006 including $2.44 million in congressional earmarks. The FY 2007 appropriations have not been passed by Congress; the president’s budget requests $15.4 million for CWD. On July 21, 2006, APHIS published its final CWD rule. The final rule added moose and all Cervus species to the previously announced deer and elk species covered in the herd certification program. It expanded the term "captive" to "farmed and captive", maintained a five-year surveillance standard for surveillance, clarified that two positive official tests are needed for a CWD diagnosis, reduced the minimum testing age to 12 months, adjusted commingling buffers, eliminated the 48-hour exemption for short-term commingling, changed the identification (ID) requirement to one official ID and one ID unique within the herd, and added the reporting of escapes and disappearances. Grandfathering of state programs will be accomplished through Memorandum of Understanding (MOUs) with the states followed by reviews of state programs for consistency with federal requirements. The interstate movement requirements maintained a "ramping up" process to reach the five year surveillance standard. An exemption was created for direct movement to slaughter. A permit will be required for interstate movement of research animals and two IDs will be required for wild cervids captured for translocation and release. Subsequent to publication of the rule, three petitions were received from organizations representing state agencies and officials challenging the interstate movement provisions in the rule and requesting a stay in the rule’s implementation. The petitions challenged the scientific basis for initially allowing the interstate movement of animals with only one or two years of surveillance. They also took issue with the federal preemption language in the rule. According to USDA legal counsel, federal preemption on interstate movement is implicit in all APHIS regulations; it was made explicit in this case in response to a comment on the proposed rule. Nevertheless, APHIS believes the petitions merit further consideration. On September 8, 2006, APHIS published a notice of delay of implementation for the rule. The petitions will be published soon for public comment. APHIS intends to resolve the issues quickly so that a final rule can be implemented as the state-federal-industry program it is intended to be.

Dr. Robert Kunkle, National Animal Disease Center (NADC), Agricultural Research Center (ARS), USDA, presented a time-specific Committee paper entitled "Experimental Transmission of Chronic Wasting Disease (CWD) of Elk (Cervus elapus nelsoni), White-tailed Deer

(Odocoileus virginianus), and Mule Deer (Odocoileus hemionus hemionus) to White-tailed Deer by Intracerebral Route. This paper is included in its entirety in these proceedings.

Dr. Michael Miller, Senior Wildlife Veterinarian, Colorado Division of Wildlife, provided an overview of recent progress in understanding various aspects of chronic wasting disease (CWD) epidemiology, diagnosis, and control. Dr. Miller used the occurrence of CWD in a moose to hypothesize that the potential natural host range of CWD may be predicted based on similarities between the native prion protein of known hosts (deer, wapiti, and moose) and other cervid species. He also reviewed findings related to CWD transmission and showed that simulation models of epidemic dynamics based on relatively simple transmission assumptions suggest that CWD is likely to persist in wild deer populations and depress population performance over time. Dr. Miller next described highlights of a new study on PrPCWD distribution in experimentally-infected mule deer that demonstrated marked genetic effects on CWD progression but not susceptibility in this species, and discussed the potential implications for CWD epidemiology. He then shared preliminary data on use of rectal mucosa biopsy to detect CWD infections in live white-tailed and mule deer, which suggest that rectal biopsy likely will be a useful herd screening test and surveillance tool provided PrP genotype data are available for sampled individuals. Dr. Miller concluded his presentation with a brief summary of unsuccessful attempts to control CWD in north central Colorado, emphasizing the challenges and obstacles that likely make eradication of CWD from the wild infeasible given present technology.


Dr. Keith Rohr presented a resolution on "The use of the ELISA test to diagnose Chronic Wasting Disease in Captive Wildlife". After discussion and modification to the original submission, the resolution was passed by the Committee and will be referred to the Committee on Nominations and Resolutions. Resolution passed by the Committee and referred to the Committee on Nominations and Resolution.

Experimental Transmission of Chronic Wasting Disease (CWD) of Elk (Cervus elaphus nelsoni), White-tailed Deer (Odocoileus virginianus), and Mule Deer (Odocoileus hemionus hemionus) to White-tailed Deer by Intracerebral Route

R.A. Kunkle, A.N. Hamir, J.M. Miller, J.A. Richt, J.J. Greenlee

National Animal Disease Center

Agriculture Research Center

United States Department of Agriculture

S.M. Hall

National Veterinary Services Laboratories, USDA-VS-APHIS

Animal and Plant Health Inspection Service

Veterinary Services

United States Department of Agriculture

E.S. Williams

Wyoming Veterinary Laboratory

University of Wyoming

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) affecting elk, white-tailed deer, and mule deer. Intra-species transmission of CWD is readily accomplished via oral administration of CWD-affected brain, and while the exact mode of natural transmission is unclear, horizontal transmission within species has been demonstrated.

The TSE’s are prion-associated diseases. Different prion strains are associated with variations in clinical course and pathology in susceptible animal hosts. To determine the potential existence of CWD pathotype strain differences, groups of five white-tailed deer were inoculated by intracerebral route (IC) with 1 ml of 10% (wt/vol) brain homogenates derived from CWD-affected elk, white-tailed deer, or mule deer. Two non-inoculated deer served as negative controls. All deer were homozygous at PrP gene polymorphic sites 95 (glutamine) and 138 (serine). Deer homozygous (glycine/glycine) or heterozygous (glycine/serine) at codon 96 were approximately equally divided between treatment groups. One deer from each treatment group was euthanized 10 months post-inoculation (PI); findings for these three deer were similar and included limited or mild spongiform encephalopathy (SE) and immunohistochemical (IHC) detection of prion in lymphoid tissue follicles and in the CNS, especially in subependymal areas. All remaining deer were euthanized at the terminal stage of disease. The clinical course of CWD appeared similar between groups. The survival period did not differ between groups, ranging from 14 to 26 months, with an average mean of 20 months. The severity of SE and magnitude of IHC staining appeared proportional to incubation period. Microscopic lesions in the CNS were typical of previously reported CWD SE, including the presence of cerebral florid plaques. IHC staining was multifocally extensive to diffuse, and was perineuronal, subependymal, and neuropil associated. Staining was pronounced in the midbrain, but relatively sparse in the hippocampus. Differences in histopathologic and IHC findings between groups were not noted. Negative control deer sacrificed at 26 months PI did not have SE and were IHC negative. The composite findings indicate the clinical course and pathology of CWD in IC challenged white-tailed deer was not influenced by species of the inoculum source or by PrP gene polymorphism at codon 96 in recipients.

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The enzyme-linked immunosorbent assay (ELlSA) for chronic wasting disease (CWD) is approved and licensed for free roaming mule deer, white tailed deer and elk. There is ample data indicating essentially equal sensitivity and specificity of ELISA tests compared to immunohistochemistry (IHC). The ELISA test can be done with faster turnaround times and is more efficient for the laboratory and requires fewer personnel than IHC. The ELISA test positives can be confirmed by IHC conducted by laboratory personnel who are experienced in identifying the obex and lymph node tissue to ensure proper tissue submission. More timely laboratory results are needed for producers to move animal product, to verify CWD status and for proper disposal of potentially CWD positive animals.


The United States Animal Health Association (USAHA) requests that the United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Veterinary Services (VS) approve the USDA licensed enzyme-linked immunosorbent assay (ELISA) test for use on cervid species within the captive wildlife industry


Animal Plant Health Inspection Service (APHIS), Veterinary Services (VS)

The United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Veterinary Services (VS) is proactive in detecting and monitoring chronic wasting disease (CWD) in the United States. The VS Center for Veterinary Biologics has approved four rapid test kits for CWD in wild deer and elk. The species and tissues for which each kit has been approved vary. APHIS has approved the kits to facilitate processing large numbers of samples collected during the hunting

season. In wild cervids (where the goal is to detect and monitor the prevalence of CWD at the population level, and where animals migrate relatively short distances), it is preferable to identify positive animals early, but not as critical if one is not detected.

Conversely, in farmed and captive populations—where the goal is to eliminate CWD, animals are often transported over long distances, and where the diagnosis of a positive animal has dire economic consequences for the owner or producer—it is extremely important to detect every positive animal and herd as early as possible and have the greatest possible confidence in that diagnosis. Therefore, the VS CWD program and the National Veterinary Services Laboratories (NVSL) have continued to use immunohistochemistry (IHC) testing methods as the "gold standard" and only diagnostic test used for CWD in farmed and captive cervids.

When evaluating farmed and captive cervid submissions for CWD, it is extremely important to be able to visualize tissue architecture because it can not be verified in enzyme-linked immunosorbent assay (ELISA) testing. Samples that do not contain the proper tissues could result in positive animals testing negative and being missed. Approximately 8 percent of the FY 2006 samples submitted for IHC testing were problematic because of location verification difficulties.

APHIS agrees that there are some circumstances when a quicker turnaround time for CWD testing is preferable—one example is slaughter surveillance testing, where product must be held pending test results. We are exploring the possibility of using rapid test kits for CWD slaughter surveillance, provided that a professional sample collection protocol can ensure confidence in the quality of the samples being submitted.

At depopulation, where carcasses may need to be held for test results before being directed to landfill, alkaline digestion, or incineration for disposal, the rapid test kits may prove to be a useful screening tool. In these cases, sample collectors are generally well-trained professionals and the consequences of spreading the disease because of missed positive results are remote. Furthermore, all animals in herd depopulations (including ELISA positives) will be tested by IHC.

APHIS does not believe that increased speed is justified (at the expense of potentially missing a positive result through improper tissue submission) during routine, on-farm surveillance testing scenarios where product is not being held pending test results.

We are currently testing approximately 15,000 farmed or captive cervid samples per year by IHC and have a network of 26 approved IHC laboratories. If evenly distributed, this equates to less than 600 IHC tests per lab per year, or approximately 22 per week. If laboratories have excessive IHC testing loads, it may be necessary for NVSL to redirect some of this testing to labs with the capacity to take additional samples.

Therefore, we do not believe that a blanket approval of CWD testing by ELISA in farmed cervids is indicated at this time. There were concerns raised during Committee

discussions and we will continue to evaluate the use of the ELISA and its use in the VS CWD program.


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